U.S. patent application number 17/598839 was filed with the patent office on 2022-06-16 for plasma source chamber for a spectrometer.
This patent application is currently assigned to Thermo Fisher Scientific (Bremen) GmbH. The applicant listed for this patent is Thermo Fisher Scientific (Bremen) GmbH. Invention is credited to Sebastian GEISLER, Ayrat MURTAZIN, Norbert QUAAS, Jan RATHKAMP, Mikhail SKOBLIN, Dirk WOHLERS, Tobias WOLF.
Application Number | 20220187212 17/598839 |
Document ID | / |
Family ID | 1000006228130 |
Filed Date | 2022-06-16 |
United States Patent
Application |
20220187212 |
Kind Code |
A1 |
QUAAS; Norbert ; et
al. |
June 16, 2022 |
PLASMA SOURCE CHAMBER FOR A SPECTROMETER
Abstract
A plasma source chamber (10) for use in a spectrometer comprises
an inner housing (11) for accommodating a plasma source (31) and an
outer housing (12) accommodating the inner housing. The outer
housing (12) comprises at least one outer air inlet opening (21) in
a first wall and at least one outer air outlet opening (22) in a
second wall. Walls of the inner housing and walls of the outer
housing define a spacing (25) so as to allow a first air flow (1)
from the at least one outer air inlet opening (21) to the at least
one outer air outlet opening (22) through the spacing (25) between
the inner housing and the outer housing. The inner housing (11)
comprises at least one inner air inlet opening (23) in a first wall
and at least one inner air outlet opening (24) in a second wall to
allow a second air flow (2) from the at least one inner air inlet
opening to the at least one inner air outlet opening through the
inner housing. Thus, an improved cooling of the outer surfaces of
the plasma source chamber is achieved.
Inventors: |
QUAAS; Norbert; (Bremen,
DE) ; MURTAZIN; Ayrat; (Bremen, DE) ; GEISLER;
Sebastian; (Bremen, DE) ; WOLF; Tobias;
(Bremen, DE) ; RATHKAMP; Jan; (Bremen, DE)
; WOHLERS; Dirk; (Bremen, DE) ; SKOBLIN;
Mikhail; (Dolgoprudny, RU) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thermo Fisher Scientific (Bremen) GmbH |
Bremen |
|
DE |
|
|
Assignee: |
Thermo Fisher Scientific (Bremen)
GmbH
Bremen
DE
|
Family ID: |
1000006228130 |
Appl. No.: |
17/598839 |
Filed: |
April 8, 2020 |
PCT Filed: |
April 8, 2020 |
PCT NO: |
PCT/EP2020/060048 |
371 Date: |
September 27, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01N 2201/022 20130101;
H05H 1/30 20130101; G01N 21/73 20130101 |
International
Class: |
G01N 21/73 20060101
G01N021/73; H05H 1/30 20060101 H05H001/30 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 10, 2019 |
GB |
1905069.9 |
Claims
1. A plasma source chamber for use in a spectrometer, the plasma
source chamber comprising: an inner housing for accommodating a
plasma, source; and an outer housing accommodating the inner
housing, wherein the outer housing comprises at least one outer air
inlet opening in a first wall and at least one outer air outlet
opening in a second wall, wherein walls of the inner housing and
walls of the outer housing define a spacing so as to allow a first
air flow from the at least one outer air inlet opening to the at
least one outer air outlet opening through the spacing between the
inner housing and the outer housing, and wherein the inner housing
comprises at least one inner air inlet opening in a first wall and
at least one inner air outlet opening in a second wall to allow a
second air flow from the at least one inner air inlet opening to
the at least one inner air outlet opening through the inner
housing.
2. The plasma source chamber according to claim 1, wherein the
walls, the inlets and the outlets are arranged such that in use the
first air flow is greater than the second air flow.
3. The plasma source chamber according to claim 1, wherein the at
least one outer air inlet opening and the at least one outer air
outlet opening are arranged in opposite walls of the outer
housing.
4. The plasma source chamber according to claim 1, wherein the at
least one outer air inlet opening is located, in use, lower than
the at least one outer outlet opening.
5. The plasma source chamber according to claim 1, wherein the at
least one outer air outlet opening is larger than the at least one
outer air inlet opening.
6. The plasma source chamber according to claim 1, wherein the at
least one outer air inlet opening extends over substantially the
width of a wall of the outer housing.
7. The plasma source chamber according to claim 1, wherein the at
least one outer air outlet opening extends over substantially the
width of a wall of the outer housing.
8. The plasma source chamber according to claim 1, wherein the at
least one inner air inlet opening and the at least one inner air
outlet opening are arranged in opposite walls of the inner
housing.
9. The plasma source chamber according to claim 1, wherein the at
least one inner air inlet opening is located, in use, lower than
the at least one inner air outlet opening.
10. The plasma source chamber according to claim 1, wherein the at
least one inner air outlet opening is larger than the at least one
inner air inlet opening.
11. The plasma source chamber according to claim 1, wherein the at
least one inner air inlet opening extends over substantially the
width of a wall of the inner housing.
12. The plasma source chamber according to claim 1, wherein the at
least one inner air outlet opening extends over substantially the
width of a wall of the inner housing.
13. The plasma source chamber according to claim 1, wherein the at
least one inner air inlet opening is in direct communication with
the spacing between the inner housing and the outer housing.
14. The plasma source chamber according to claim 1, wherein the at
least one inner air inlet opening is connected to a duct which
extends through the spacing and through a wall of the outer housing
so as to allow a flow of air from outside the outer housing.
15. The plasma source chamber according to claim 1, wherein the at
least one inner air outlet opening is in direct communication with
the spacing between the inner housing and the outer housing.
16. The plasma source chamber according to claim 1, wherein the at
least one inner air outlet opening is connected to a duct which
extends through the spacing and through a wall of the outer housing
so as to allow a flow of air to the outside of the outer
housing.
17. The plasma source chamber according to claim 1, wherein the
inner housing is removable.
18. The plasma source chamber according to claim 1, further
comprising a shielding element for covering at least one wall of
the outer housing, said shielding element and said wall defining a
further spacing so as to allow a third flow of air between said
shielding element and the outer housing.
19. The plasma source chamber according to claim 18, wherein the
shielding element is arranged for covering two substantially
perpendicular walls of the outer housing, the further spacing
extending between said shielding element and said walls, one of
said walls preferably being, in use, a top wall.
20. The plasma source chamber according to claim 1, wherein the
inner housing has at least one further air inlet opening in a wall
which is, in use, a bottom wall.
21. The plasma source chamber according to claim 1, wherein further
openings are provided in walls of both the inner housing and outer
housing to accommodate a plasma source and at least one periscopic
viewing element.
22. The plasma source chamber according to claim 1, arranged for
accommodating a vertical plasma source.
23. The plasma source chamber according to claim 1, arranged for
accommodating a horizontal plasma source.
24. The plasma source chamber according to claim 1, wherein the
plasma source is an inductively coupled plasma source, a flame
source, a microwave-induced plasma source, or an electro-thermo
ionization source.
25. The plasma source chamber according to claim 1, further
comprising an inner door for the inner housing and an outer door
for the outer housing.
26. The plasma source chamber according to claim 25, wherein at
least one of the inner door and the outer door is a sliding
door.
27. The plasma source chamber according to claim 25, wherein the
inner door and the outer door are connected such that opening or
closing the outer door also opens or closes the inner door.
28. A spectrometer comprising a plasma source chamber, the plasma
source chamber comprising: an inner housing for accommodating a
plasma source; and an outer housing accommodating the inner
housing, wherein the outer housing comprises at least one outer air
inlet opening in a first wall and at least one outer air outlet
opening in a second wall, wherein walls of the inner housing and
walls of the outer housing define a spacing so as to allow a first
air flow from the at least one outer air inlet opening to the at
least one outer air outlet opening through the spacing between the
inner housing and the outer housing, and wherein the inner housing
comprises at least one inner air inlet opening in a first wall and
at least one inner air outlet opening in a second wall to allow a
second air flow from the at least one inner air inlet opening to
the at least one inner air outlet opening through the inner
housing.
29. The spectrometer according to claim 28, which is: an emission
spectrometer, or an atomic absorption spectrometer, or a mass
spectrometer.
30. The spectrometer according to claim 28, which is a plasma
optical emission spectrometer.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a plasma source chamber for
a spectrometer. More in particular, the present invention relates
to a plasma source chamber for use in a spectrometer which is
capable of accommodating a plasma source without requiring an
active cooling element within the chamber.
BACKGROUND OF THE INVENTION
[0002] It is well known to use plasma sources in spectrometers,
such as emission spectrometers and mass spectrometers. A plasma
source, such as an inductively coupled plasma (ICP) source,
produces a plasma in which atoms and molecules can be ionized. In
such a plasma, extremely high temperatures may occur, such as
temperatures of 8,000 K or even 10,000 K. In conventional
spectrometers, plasma sources were accommodated in large chambers,
thus allowing relatively large distances between the plasma and the
walls and other parts of the chamber. As the users of spectrometers
increasingly desire more compact instruments, the dimensions of
plasma source chambers have decreased, leading to smaller distances
between the plasma source and other parts. It will be understood
that this creates problems relating to temperatures and temperature
gradients.
[0003] It is well known to use an air flow inside a plasma chamber
for cooling. The Thermo Scientific.TM. iCAP.TM. 7000 ICP-OES
Analyzer system produced by Thermo Fisher Scientific.RTM., for
example, has a plasma chamber in which a plasma torch is
accommodated and in which an air flow is used for cooling. An air
outlet opening is provided in the top wall of the plasma chamber,
above the plasma torch, while an air inlet opening is provided in
the bottom wall, near a side wall, thus allowing an air flow from
the bottom to the top of the chamber, past the plasma torch.
Although this arrangement works well for a vertical torch that is
viewed radially, it is less suitable for axial viewing of a
vertical torch. For this reason, the torch of the iCAP.TM.7000
system is arranged horizontally while retaining the top air outlet
and allowing axial viewing from the side in dual view
arrangements.
[0004] To retain the freedom to mount the plasma torch either
horizontally or vertically, as desired, in both single view and
dual view arrangements, it would be possible to provide a top air
outlet at the side of the plasma chamber, thus freeing up space
above the plasma torch. However, an air outlet away from the center
of the plasma chamber would give rise to crossflows of air, which
may disturb the plasma and lead to instability of the plasma
source. However, the air flow should be sufficiently large to cool
the plasma chamber such that its outer surface does not constitute
a safety hazard, even when the dimensions of the plasma chamber are
limited.
[0005] Japanese patent application JP2005-205296 discloses an ICP
spectrometer with an exhaust gas cooling apparatus. The plasma
chamber of JP2005-205296 has an elbow-shaped pre-cooling pipe which
is fixed to a pre-cooler. A gas cooler disposed downstream of a
pre-cooling pipe contains a water-cooled heat exchange coil. An
exhaust fan is also provided. The elbow shape of the cooling pipe
prevents a line of sight between the inlet and the outlet, which is
in some applications undesirable. In addition, the plasma chamber
of JP2005-205296 requires a precooler, a gas cooler and a fan,
making the arrangement complicated and relatively expensive.
SUMMARY OF THE INVENTION
[0006] The present invention seeks to overcome the disadvantages of
the prior art and to provide a plasma source chamber for a
spectrometer which may be compact, which allows a vertical plasma
source to be used and which does not require an active cooling
mechanism. In particular, the present invention seeks to provide a
plasma source chamber which provides sufficient cooling of its
outer surface without requiring a strong air flow which disturbs
the plasma.
[0007] Accordingly, the present invention provides a plasma source
chamber for use in a spectrometer, the plasma source chamber
comprising an inner housing for accommodating a plasma source, and
an outer housing accommodating the inner housing, wherein the outer
housing comprises at least one outer air inlet opening in a first
wall and at least one outer air outlet opening in a second wall,
wherein walls of the inner housing and walls of the outer housing
define a spacing so as to allow a first air flow from the at least
one outer air inlet opening to the at least one outer air outlet
opening through the spacing between the inner housing and the outer
housing, and wherein the inner housing comprises at least one inner
air inlet opening in a first wall and at least one inner air outlet
opening in a second wall to allow a second air flow from the at
least one inner air inlet opening to the at least one inner air
outlet opening through the inner housing.
[0008] By providing both an inner housing and an outer housing, a
double-layered heat protection structure is obtained. By providing
a spacing between the inner housing and the outer housing, a direct
heat transfer between the inner housing and the outer housing is
avoided, thus significantly improving the heat insulation. In
addition, the spacing allows an air flow to pass between the inner
housing and the outer housing, thus cooling the outer housing with
air that does not pass through the inner housing. As a result, the
air flow that does pass through the inner housing can be limited in
volume and velocity, while the temperature of the outer housing can
be limited to values which comply with safety regulations, even
when the interior volume of the plasma source chamber is small. In
particular, the invention allows total air flow rates of less than
250 m.sup.3/h to be used in certain embodiments. The plasma source
chamber of the invention may be suitable for both radial and axial
observation of the plasma, also when a vertical plasma torch is
used.
[0009] In advantageous embodiments of the invention the walls, the
inlets and the outlets are arranged such that in use the first air
flow is greater than the second air flow. That is, in such
embodiments the air flow through the outer housing is greater in
volume and/or air speed than the air flow through the inner
housing. Conversely, the air flow through the inner housing is
smaller than the air flow through the outer housing, thus
preventing the plasma being disturbed by the air flow. This may be
achieved by the relative dimensions of the air inlet openings and
the air outlet openings, and on their relative orientations.
[0010] The present invention is based upon the insight that the air
flows in a plasma source chamber should be guided in such a way
that the outer surface of the plasma source chamber is cooled
sufficiently. The present invention benefits from the further
insight that the air flow at and around the plasma torch should be
limited in volume and velocity so as to avoid the plasma being
disturbed by the air flow.
[0011] The present invention also benefits from the still further
insight that providing a spaced inner and outer housing allows an
air flow through the spacing and hence allows the outer surface to
be cooled while leading air away from the plasma in the inner
housing.
[0012] In order to avoid the plasma being disturbed by the air
flow, it is preferred that the air flow through the inner housing
is smaller than the air flow through the spacing between the inner
housing and the outer housing. In other words, the main air flow is
led around instead of through the inner housing.
[0013] Both the inner housing and the outer housing have at least
one air inlet opening in a first wall and at least one air outlet
opening in a second wall, the first wall and the second wall
preferably being different walls, such as opposite side walls. In
either the inner housing and the outer housing, or in both, the at
least one air inlet opening may be located, in use, lower than the
at least one outlet opening. That is, the inlet openings may be
located at and/or in a bottom wall while the outlet openings may be
located at and/or in a top wall of the inner and outer housing when
the plasma chamber is in use. In this way, the natural air flow is
facilitated, as the air will heat up considerably as it passes
through the plasma chamber. As air expands when it heats up, the
air outlet openings may advantageously be larger than the air inlet
openings, that is, the air outlet openings may have a larger
cross-section, for example.
[0014] The at least one outer air inlet opening, that is, the air
inlet opening of the outer housing, may extend over substantially
the width of a wall of the outer housing. Similarly, the at least
one outer air outlet opening, that is, the air outlet opening of
the outer housing, may extend over substantially the width of a
wall of the outer housing. Additionally, or alternatively, at least
one air inlet opening of the inner housing and/or at least one air
inlet opening of the outer housing may extend over substantially
the width of a wall of the inner housing.
[0015] In the plasma source chamber according to the invention, the
at least one inner air inlet opening may be in direct communication
with the spacing between the inner housing and the outer housing.
As a result, the air flow through the inner housing (which may be
referred to as second air flow) may be derived from the air flow
through the spacing between the inner housing and the outer housing
(which may be referred to as first air flow). That is, part of the
(first) air flow through the spacing branches off to constitute the
(second) air flow through the inner housing.
[0016] Alternatively, the at least one inner air inlet opening may
be connected to a duct which extends through the spacing and
through a wall of the outer housing so as to allow an air flow from
outside the outer housing. In such embodiments, the (first) air
flow through the spacing and the (second) air flow through the
inner housing are separate air flows.
[0017] Similarly, the at least one inner air outlet opening may be
in direct communication with the spacing between the inner housing
and the outer housing. That is, the (second) air flow through the
inner housing may join the (first) air flow in the spacing,
preferably at or near an air outlet opening of the outer housing.
Alternatively, or additionally, the at least one inner air outlet
opening may be connected to a duct which extends through the
spacing and through a wall of the outer housing so as to allow an
air flow to the outside of the outer housing.
[0018] In a particularly advantageous embodiment, the inner housing
is removable. That is, the inner housing may be removed from the
plasma chamber and may therefore be removably attached to the outer
housing. By providing a removable inner housing, the interior of
the plasma chamber can more easily be cleaned, which may be
necessary due to a built-up of deposits in the inner housing. In
addition, by providing a removable inner housing, the inner housing
can be replaced when necessary.
[0019] In an embodiment, the plasma source chamber may further
comprise a shielding element located outside the outer housing for
covering at least one wall of the outer housing, said shielding
element and said wall defining a further spacing so as to allow a
third flow of air between said shielding element and the outer
housing. The further spacing and the associated air flow provides
cooling of the exterior of the outer housing, while providing
additional heat insulation due to the additional layer constituted
by the shielding element. The shielding element may be arranged for
covering two substantially perpendicular walls of the outer
housing, the further spacing extending between said shielding
element and said walls, one of said walls preferably being, in use,
a top wall. The shielding element may face the (typically
temperature sensitive) optics section of the spectrometer.
[0020] As mentioned above, both the inner housing and the outer
housing may have more than one air inlet opening and/or more than
one air outlet opening. In particular, the inner housing may have
at least one further air inlet opening in a wall which is, in use,
a bottom wall. Further openings may be provided in walls of both
the inner housing and outer housing to accommodate a plasma source
and at least one viewing element, such as a periscope, for viewing
the plasma. As there is no need for an air outlet opening
immediately above the plasma torch in such an arrangement, an axial
viewing element can be located substantially above the plasma
torch. An axial viewing element may be purged by a supply of argon
to provide a purged optical path.
[0021] The plasma source chamber according to the present invention
may comprise an inner door for the inner housing and an outer door
for the outer housing, which doors may be coupled to provide a
combined motion of the doors. At least one of the inner door and
the outer door may be a sliding door. In an embodiment, both the
inner door and the outer door are sliding doors.
[0022] The plasma source chamber according to the present invention
may advantageously be arranged for accommodating a vertical plasma
source. However, embodiments accommodating a horizontal plasma
source are also possible. In either orientation, the plasma source
may be an inductively coupled plasma (ICP) source. Other sources,
such as a flame source, an MIP (Microwave-Induced Plasma) source,
or an ETA (Electro-Thermo Ionization) source, may also be arranged
horizontally or vertically in the source chamber of the present
invention.
[0023] The present invention additionally provides a spectrometer,
such as an emission spectrometer, more in particular an optical
emission spectrometer, or a mass spectrometer, comprising a plasma
source chamber as described above. An emission spectrometer
according to the invention may further comprise a sample
introduction system for introducing a sample to be analyzed into
the plasma and a detection unit for detecting the emission of the
plasma. A mass spectrometer according to the invention may further
comprise a skimmer cone, a sampling cone, at least one mass filter,
such as a quadrupole mass filter, ion optics, and a detection unit
for detecting ions. The spectrometer provided by the invention may
alternatively be an atomic fluorescence spectrometer or an atomic
absorption spectrometer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 schematically shows an exemplary embodiment of a
plasma source chamber according to the prior art.
[0025] FIG. 2 schematically shows a first exemplary embodiment of a
plasma source chamber according to the present invention.
[0026] FIG. 3 schematically shows a second exemplary embodiment of
a plasma source chamber according to the present invention.
[0027] FIG. 4 schematically shows an embodiment of an inner housing
of a plasma source chamber according to the present invention.
[0028] FIG. 5 schematically shows an embodiment of an outer housing
of a plasma source chamber according to the present invention.
[0029] FIG. 6 schematically shows an embodiment a plasma source
chamber according to the present invention.
[0030] FIG. 7 schematically shows an exemplary embodiment of an
emission spectrometer comprising a plasma source chamber according
to the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0031] A plasma chamber according to the prior art is schematically
illustrated in the cross-sectional view of FIG. 1. A plasma chamber
(or plasma source chamber) of this kind is used, for example, in
the iCAP 7000.TM. mass spectrometer manufactured by Thermo Fisher
Scientific.RTM.. The plasma chamber 10' is shown to comprise a
housing 15 in which a plasma torch 31 is accommodated. The plasma
torch 31 is provided with an RF electrical induction coil 38 which
is arranged around a part of the length of the plasma torch 31. The
RF electrical induction coil 38 serves as heating element to
generate a plasma. A viewing element 39 protrudes from a side wall
of the plasma chamber to view the plasma in use from the side. An
exhaust pipe 18 is arranged on the top wall of the plasma chamber
10' in direct communication with an air outlet opening 29, which is
located above the plasma torch 31. An air inlet opening 21 is
provided in the bottom wall of the plasma chamber, adjacent a side
wall.
[0032] The location of the exhaust pipe 18 prevents a viewing
element to be located in the top wall of the plasma chamber, which
is less convenient in some applications. In addition, the air flow
5 through the plasma chamber is from the air inlet opening 21 past
the plasma above the plasma torch 31 to the air outlet opening 29.
It will be understood that the air flow cannot be too strong, or
the plasma will be disturbed.
[0033] The exemplary embodiment of a plasma source chamber 10
according to the invention which is schematically shown in the
cross-sectional view of FIG. 2 comprises an inner housing (or inner
chamber) 11 which is accommodated in an outer housing (or outer
chamber) 12. In the inner housing 11, a plasma torch 31 is arranged
which, in use, can produce a plasma 30. Above the plasma torch 31,
a viewing element 32 is arranged for axially viewing the plasma.
The viewing element 32 is, in the embodiment shown, constituted by
a pipe through which a gas is fed to provide a purged optical path.
The gas is preferably an oxygen-free dry gas, such as argon (Ar),
to allow the transmission of deep ultra-violet (UV) light through
the viewing element 32. It is noted that in the embodiment shown,
the plasma torch is arranged, in use, vertically in the inner
housing 11, and that the viewing element 32 is arranged
substantially axially above the plasma torch 31.
[0034] The inner housing 11 is provided with an air inlet opening
23 and an air outlet opening 24, which are in the embodiment shown
arranged in opposite walls of the inner housing 11, so as to allow
an air flow 2 through the inner housing 11. Additional air inlet
openings may be present in the walls of the inner housing, such as
the air inlet openings 23A arranged in the bottom wall adjacent the
plasma torch 31, which allow additional air flows 2A through the
inner housing. Similarly, additional air outlet openings may be
provided. In the embodiment shown, the air outlet opening 24 is
located, in use, higher than the air inlet openings 23 and 23A so
as to assist a natural flow of the air which is heated by the
plasma. However, in some embodiments the air inlet openings may be
located at substantially the same height, or even higher than the
air outlet openings.
[0035] The outer housing 12 is provided, in the embodiment shown,
with an air inlet opening 21, an air outlet opening 22 and an
additional air outlet opening 22A. in the embodiment shown, the air
inlet and outlet openings 21 and 22 are arranged at opposite walls
of the outer housing 12, while the air outlet openings 22 and 22A
are arranged higher, in use, than the air inlet opening 21, to
assist the natural flow of the heated air through the outer
housing. However, in some embodiments the air inlet openings may be
located at substantially the same height, or even higher than the
air outlet openings.
[0036] In accordance with the invention, a spacing 25 is present
between the inner housing 11 and the outer housing 12, which allows
air flows 1 through the outer housing 12 but substantially around
the inner housing 11. It can be seen in the embodiment of FIG. 2
that air flows 1 are present around all four walls of the inner
housing 11 which are shown in FIG. 2.
[0037] It will be understood that such air flows may also be
present in spacings (not shown in FIG. 2) between the respective
front walls of the inner housing and the outer housing, and/or
between the respective back walls of the inner housing and the
outer housing. In some embodiments, no spacings through which air
flows are provided at the front and/or the back of the plasma
source chamber, only spacings between at least one pair of side
walls (that is, between respective side walls of the inner housing
and the outer housing) and at least one pair of upper walls (that
is, between respective upper walls or covers of the inner housing
and the outer housing).
[0038] By providing a spacing between the inner housing and the
outer housing, air can flow between the inner housing and the outer
housing. In addition, the double wall thus provided above the
plasma torch provides a double shielding of any object above the
plasma chamber from the heat of the plasma torch.
[0039] In accordance with a further aspect of the invention, the
inner housing 11 and the outer housing 12 are arranged in such a
way that the air flow 1 through the spacing between the inner
housing and the outer housing is greater than the air flow 2
through the inner housing 11. That is, the (second) air flow 2
through the inner housing 11 has for example a smaller volume rate
than the (first) air flow 1 through the spacing 25. By passing a
smaller part of the total air flow through the inner housing 11 and
a larger part through the spacing 25, a strong air flow past the
plasma and hence a disturbance of the plasma is avoided, while
providing an excellent cooling effect of both the inner and the
outer housing.
[0040] A smaller air flow passing through the inner housing can be
obtained by a suitable choice of (relative) dimensions. In
particular, the diameters and/or surface areas of air inlet opening
23 and of air outlet opening 24 of the inner housing 11 as well as
the diameters and/or surface areas of air inlet opening 21 and of
air outlet openings 22 and 22A of the outer housing 12 are chosen
such that the first air flow 1 through the spacing is greater than
the second air flow 2 through the inner housing. Also, the relative
orientations of the various openings contribute in providing the
desired air flows. The orientation of the inlet opening 23, for
example, is substantially perpendicular to the longitudinal
direction of the spacing 25 at the location of the inlet opening
23. As a result, the air flow through the spacing 25 is not
directed to but along the inlet opening 23. This contributes to
reducing the air flow 2 through the inner housing relative to the
air flow through the spacing.
[0041] In the exemplary embodiment shown, the spacing between the
inner housing 11 and the outer housing 12 has a width of
approximately 3 cm, both at the side wall where the opening 23 is
located and at the top walls. The air inlet opening 21 and the air
outlet opening 22 both have, in the embodiment shown, an area of
approximately 48 cm.sup.2, while the air inlet opening 23 has an
area of approximately 24 cm.sup.2 and the air outlet opening 24 has
an area of approximately 52 cm.sup.2. It can thus be seen that the
area of the air inlet opening 23 of the inner housing is
approximately half the size of the area of the air inlet opening 21
of the outer housing, while the area of the air outlet opening 24
of the inner housing is more than twice the size of the air inlet
opening 23 of the inner housing, in this example approximately 2.2
times as large. The additional air outlet opening 22A may have an
area of approximately 11 cm.sup.2, that is, approximately one
quarter of the area of the air outlet opening 22.
[0042] It will be understood that the dimensions given above are
only examples and that actual dimensions of a plasma source chamber
according to the invention may vary, also in dependence on their
relative orientations. For example, the air inlet opening 23 of the
inner housing is, in the example shown, arranged at a right angle
relative to the air inlet opening 21 of the outer housing. If this
angle were more or less than 90.degree., the area of the air inlet
opening 23 of the inner housing could be adapted to achieve the
same air flow 2. Similarly, the additional air inlet openings 23A
of the inner housing are, in the example shown, arranged at a right
angle relative to the air flow 1 through the spacing and may have
other dimensions when arranged at a different angle.
[0043] The ratio of the areas of the air inlet opening 23 of the
inner housing and of the air inlet opening 21 of the outer housing
need not be approximately equal to 0.5 but could be in a range from
0.1 to 2.0, or in a range from 0.25 to 1.0, for example. Similarly,
the ratio of the areas of the air outlet opening 24 of the inner
housing and of the air inlet opening 23 of the inner housing need
not be approximately equal to 2 but could be in a range from 1 to
4, or in a range from 1.5 to 3, for example.
[0044] Both the shielding effect and the air-cooling effect may be
further improved by providing a shielding member, as shown in FIG.
3. The exemplary embodiment of FIG. 3 also comprises an inner
housing 11 and an outer housing 12, as the embodiment of FIG. 2. In
addition, the embodiment of FIG. 3 comprises a shielding member 13
which extends, in the embodiment shown, over a side wall and the
top wall so as to provide an additional shielding layer between the
plasma source 31 and any objects located above the plasma chamber
10. In addition, the shielding element 13 can be spaced apart from
the outer housing 13 to provide an additional spacing 26 through
which an additional air flow 3 can flow. This additional air flow 3
provides additional cooling of the outer surface of the plasma
chamber, thus resulting in a lower temperature.
[0045] It is noted that the shielding member 13 may, in some
embodiments, extend over more than two wall parts than shown in
FIG. 3, and may for example also extend over a back wall. Thus, the
shielding element may serve as an additional outer housing.
Alternatively, the shielding element may extend over only a single
wall part, for example only the top wall, or possibly only a side
wall.
[0046] As can be seen in FIG. 3, the shielding element 13 extends
substantially in parallel to the walls of the outer housing 12 at
some distance (for example a few centimeters or a few millimeters)
from those walls, leaving a spacing 26 between the outer housing 12
and the shielding element 13. In accordance with the invention,
this additional spacing 26 may advantageously be used to pass a
further air flow through the plasma chamber 10. An additional air
inlet opening 27 is provided to allow an additional or third air
flow 3 to pass through the spacing 26 between the outer housing 12
and the shielding element 13. In the embodiment shown, an opening
28 located adjacent the (outer) air outlet opening 22 constitutes
the air outlet opening of the additional spacing 26. In the
embodiment of FIG. 3, a common air outlet opening or exhaust
opening 29 is provided through which the first air flow 1, the
second air flow 2 and the third air flow 3 exit the plasma
chamber.
[0047] In the exemplary embodiment shown, the air outlet opening 29
has an area of approximately 130 cm.sup.2 while the air inlet
opening 27 has an area of approximately 8 cm.sup.2, resulting in a
ratio of approximately 16. Of course, other ratios are possible,
for example ratios in a range from approximately 4 to approximately
64, or from approximately 8 to approximately 32.
[0048] An embodiment of an inner housing 11 is schematically shown
in perspective view in FIG. 4. The inner housing 11 is shown to
have an air inlet opening 23 in one side wall and an air outlet
opening 24 in another side wall, opposite the first side wall. It
can be seen that in the embodiment shown, the air outlet opening 24
is located higher than the air inlet opening 23.
[0049] The inner housing 11 of FIG. 4 further comprises a viewing
opening 34 in the top wall to accommodate an axial plasma viewing
element (32 in FIGS. 1 and 2) which can constitute a purged optical
path. The viewing opening 34 is preferably as small as possible.
The inner housing 11 also comprises a plasma torch opening 35 to
accommodate a plasma torch (31 in FIGS. 2 and 3). The inner housing
may comprise further openings, such as further air inlet openings
23A (see also FIGS. 2 and 3) surrounding the plasma torch opening
35. The back wall of the embodiment shown is provided with an
opening 36 for accommodating a radial plasma viewing element (39 in
FIG. 6). It will be understood that the opening 36 for
accommodating a radial plasma viewing element could be arranged in
any side wall instead. In the embodiment shown, a side wall is
provided with a video camera opening 48 for allowing a plasma video
camera to view the plasma. In the embodiment shown, the opening 48
is arranged below the air outlet opening 24. In some embodiments,
such a video camera opening may be omitted.
[0050] An embodiment of an outer housing 12 according to the
invention is illustrated in the perspective view of FIG. 5. The
outer housing is shown to have an air inlet opening 21 at a bottom
corner, in both a side wall and a bottom wall, as well as an air
outlet opening 22 located in the upper part of a side wall,
opposite the side wall adjacent the air inlet opening 21. An
opening 35A, corresponding with the opening 35 in the inner housing
11 (see FIG. 4), is provided to accommodate the plasma torch 31
(see FIGS. 1 & 2). Two adjacent openings 37A and 37B in the top
wall of the outer housing 12 are provided to accommodate a radial
plasma viewing element, such as a periscope, and an axial plasma
viewing element (32 in FIGS. 1 & 2) respectively. The opening
37A in the outer housing 12 corresponds with the opening 34 in the
inner housing 11 (see FIG. 4). An opening 42 in a side wall serves
to accommodate an RF electrical heating element or RF induction
coil (38 in FIGS. 2 & 3) and corresponds with the opening 23 in
the inner housing 11 (see FIG. 4). A radial viewing element can be
accommodated by opening 37B in the outer housing 12 and opening 36
in the inner housing 11. A side wall is provided with a video
camera opening 49 for allowing a plasma video camera to view the
plasma. The opening 49 in the outer housing is, in use, aligned
with the corresponding video camera opening 48 in the inner housing
(see FIG. 4). In the embodiment shown, the opening 49 is arranged
below the air outlet opening 22. In some embodiments, such a video
camera opening 49 may be omitted. A ridge 41 at the top of the back
wall and front wall of the outer housing 12 defines the spacing (26
in FIG. 3) between the outer housing and the shielding element (13
in FIG. 3).
[0051] The inner housing and the outer housing are preferably made
of metal, such as stainless steel or aluminium. The inner housing
and/or the outer housing may be produced by milling, casting, or a
combination of sheet metal cutting, bending and welding.
[0052] The inner housing may be removable so as to allow cleaning
and/or replacement. This is advantageous as sample nebulization in
the plasma torch will inevitably result in materials being
deposited in the plasma chamber, that is, in the inner housing 11.
A removable inner housing is easier to clean and may be replaced
when cleaning is not or no longer feasible.
[0053] An exemplary embodiment of a plasma source chamber according
to the invention is schematically shown in the cross-sectional view
of FIG. 6. The plasma source chamber 10 of FIG. 6 is shown to
comprise an inner housing 11 and an outer housing 12, between which
a spacing 25 is present. A plasma torch 31 provided with an RF coil
38 protrudes through an opening (35 in FIG. 4 in the bottom wall of
the inner housing 11, while a viewing element 32 protrudes through
an opening (34 in FIG. 4) in the top wall of the inner housing 11.
The viewing element 32 enters the outer housing 12 through a
further opening (37A in FIG. 5). A periscopic viewing element 39
protrudes through an opening (37B in FIG. 5) in the top wall of the
outer housing 12 and through an opening (36 in FIG. 4) in a back
wall of the inner housing 11. The periscopic viewing element 39
allows radial viewing of a plasma generated by the plasma torch 31.
Axial viewing of the plasma is, in this embodiment, possible by
viewing through the viewing element 32. It can be seen that the
viewing element 39 is arranged in the spacing between the inner
housing 11 and the outer housing 12.
[0054] The inner housing 11 is, in the embodiment shown, closed off
by a door 45. Similarly, the outer housing 12 is closed off by a
door 46. The inner door 45 and the outer door 46 may for example be
hinged and/or removable. They may be connected by a mechanism
allowing the doors 45 and 46 to be moved together, for example such
that when the outer door 46 is opened or closed by an operator, the
inner door is opened or closed respectively by the mechanism
connecting the inner door and the outer door. At least one of the
doors 45 and 46 may be a sliding door. In an embodiment, both the
inner door 45 and the outer door 46 are sliding doors.
[0055] The plasma source chamber of the present invention is
particularly suitable for emission spectrometers, but may also be
applied in other spectrometers, such as mass spectrometers and
atomic absorption spectrometers. Emission spectrometers in which
the invention may be utilized are, for example, optical emission
spectrometers and atomic fluorescence spectrometers. Although the
source chamber is described here with reference to a plasma source
(that is, an ICP torch), the invention is not so limited and may
also be used with a flame source, an MIP (Microwave-Induced Plasma)
source, or an ETA (Electro-Thermo Ionization) source.
[0056] An emission spectrometer comprising a plasma source chamber
according to the invention may further comprise a plasma torch, a
gas (e.g. argon) source, a sample introduction system for
introducing a sample to be analyzed into the plasma, and a detector
arrangement for detecting emitted light. An exemplary embodiment of
an emission spectrometer is schematically illustrated in FIG. 7,
where the spectrometer 100 is shown to comprise a plasma chamber 10
and an analyzer and detector unit 60, which are coupled by a light
duct 50. The plasma chamber 10 according to the invention may be
the plasma chamber illustrated in FIG. 2 or 3, for example. The
analyzer and detector unit 60 may include a detector unit for
detecting emitted light according to the prior art, for example an
optical analyzer and/or an optical detection system.
[0057] The light duct 50 may be constituted by the axial and radial
viewing elements described above, such as the viewing element 32
and the periscope 39 protruding into the inner housing 11 through
the openings 34 and 36 respectively (see FIGS. 4 & 6).
[0058] It will be understood by those skilled in the art that the
invention is not limited to the embodiments shown and that many
modifications and additions can be made without departing from the
invention as defined in the appending claims.
* * * * *